The herein disclosed invention is directed to chlorine dioxide formulations to be applied as disinfectants, deodorants, topical preparations and for like uses. More specifically, the invention is involved with the preparation gels of chloride dioxide to be used as disinfectants, deodorants and the like.
While there is much literature describing chloride dioxide gels, there is a need in the industry for gel products with controlled amounts of chlorine dioxide and which are easy to prepare. In addition to ease of preparation, there is a need for gel compositions with high concentrations of chlorine dioxide.
The gums employed as the gels or thickeners of this invention are generally supplied as powders and with the addition of water, thicken and become a gel.
The patent literature contains references to the use of gels for various applications ranging from a biocidal wound dressing, skin sterilants, veterinarian applications, treatment of skin conditions such as psoriasis, fungal infections, eczema, dandruff, acne, genital herpes lesions, and leg ulcers. Chlorine dioxide gels made in situ by mixing a chlorite containing gel with a lactic acid gel have been cited for prevention of transmission of HIV virus. Gels have also been cited as anti-inflammatory agents for reducing various tissue inflammations.
A review of the patent literature on the topic of the preparation of chlorine dioxide containing gels, discloses prior art patents which involve the use of sodium chlorite as the precursor for chlorine dioxide preparations, along with some method of converting said chlorite to chlorine dioxide at the time of use.
The one patent which claims chlorine dioxide as an actual component in a gel is the Hutchings Patent, U.S. Pat. No. 4,861,514. Hutchings mixes chlorite and xe2x80x9cinitiatorxe2x80x9d. Included among the xe2x80x9cinitiatorsxe2x80x9d is hydroxalklycelluloses, alkali metal alginates, xanthan gum, cargeenen, agar and compounds containing an aldehyde substituent group. Methyl cellulose and sodium carboxymethylcellulose were found not to be initiators. The sodium chlorite disclosed in the patent is used at a concentration of 0.01 to 1% by weight, and the initiator is used at levels greater than 0.05, and preferably above 0.1%. Dyes, perfumes and reducing sugars were also included in the mix. Hutchings claims a chlorine dioxide equilibrium concentration formed within a week of 0.1 to about 10 ppm, with a preferable concentration 0.1 to 2 ppm (column 7, line 9). The patent claims disinfection at greater than 1 ppm chlorine dioxide, and cleaning and sanitizing at about 2 ppm. The chlorine dioxide achieves an equilibrium at a low concentration. With the equilibrium concentration of chlorine dioxide is from 0.1 to about 10 ppm and preferably 0.1 to 2 ppm, it can be readily discerned that the concentration of chlorine dioxide taught by Hutchings does not come close to that desired in the present invention.
U.S. Pat. No. 4,861,514 cites formation of chlorine dioxide from chlorite and xanthan gum initiator. As chlorine dioxide reacts with organics, or decomposes spontaneously, chlorite is one of the decomposition products. Formed chlorite would be encouraged to reform chlorine dioxide by reaction with the acid functionality inherent in the xanthan gum, supporting the claim of gel stability using xanthan gum. Hutchings (U.S. Pat. No. 4,861,514) actually uses this chemistry to make his chlorine dioxide in situ. This stability is in contrast to the behavior of xanthan gum in the presence of other oxidants, such as persulfates, peroxides and hypochlorites, all of which depolymerize xanthan gum. As manufactured either as a 25% aqueous solution, or an 80% solid, sodium chlorite contains alkalinity to provide chemical stability. The chlorite is inert and does not convert to chlorine dioxide in a high pH environment. Addition of acid is required to promote conversion to chlorine dioxide. If the acidity is provided by xanthan gum alone, without the addition of any other organic or inorganic acids, then the amount of chlorite which can be included in the mix is limited, since the accompanying alkalinity of the chlorite partially neutralizes the acidity of the xanthan gum, preventing conversion of chlorite to chlorine dioxide. This limits the final concentration of chlorine dioxide which can be prepared in the absence of additional added acid to less than 200 ppm. Hutchings does not state this, but he is claiming only very dilute chlorine dioxide systems, and therefore is out of the range of gel concentration possible with the herein disclosed invention.
Crotty et al in U.S. Pat. No. 3,741,805 teaches a cleaning and sanitizing composition containing xanthan gum. Chlorine compounds are mentioned, but chlorine dioxide is not mentioned.
Iwahashi in U.S. Pat. No. 5,360,574 discloses a polyethylene-imine gel system containing chlorine dioxide. The system with the gel is actually a chlorite which is stabily stored in alkali and becomes active in acid (column 1). Iwakhashi is not, in fact, pertinent for while the patent refers to xe2x80x9cstabilized chlorine dioxidexe2x80x9d the product of the patent is actually a solution of sodium chlorite which has an alkaline pH. This high pH is necessary in order to insure the stability of the product. In short, the Iwakhashi product is sodium chlorite and not chlorine dioxide.
In brief, the prior art processes, unlike the instant invention, do not start with chlorine dioxide per se in solution and thicken, but rather start with chlorite which when mixed with an acid-containing gel partially converts to chlorine dioxide after mixing.
This invention has for an object the efficient preparation of chlorine dioxide gels.
Another object of this invention is the preparation of chlorine dioxide formulations in chlorine dioxide concentrations not attained by the prior art.
A significant object of this invention is to prepare a gel composition with high concentrations of chlorine dioxide.
These and other objects of the present invention will become apparent from a reading of the following specification.
The herein disclosed invention sets forth the novel methods for preparing higher concentrations of chlorine dioxide gel compositions. Involved are two types of chlorine dioxide gels, namely, those formed directly from aqueous chlorine dioxide solutions and added thickeners; and those formed by adding a specific thickener to dilute chlorite solutions, and having the chlorine dioxide generated spontaneously on storage.
Gels of this invention are novel in that the chlorine dioxide solution is prepared before the gelling action takes place, so that the concentration of the final gel can be set to any desired level beforehand by using a chlorine dioxide solution with a concentration appropriate for the intended application. The gels may be used as is without any need for additional mixing or preparation. This method allows preparation of gels with a wide range of concentrations. The use of xanthan gum as the thickener is most preferred because this polysaccharide has acid functionality which contributes to the stability of the chlorine dioxide in the gel.
Gels using various quantities of xanthan gum thickener and aqueous chlorine dioxide were prepared. It was observed that xanthan gum appeared to improve chlorine dioxide storage stability. Systems of aqueous chlorine dioxide mixed with guar gel, xanthan gel, and a mix of guar and xanthan gel all retained high levels of chlorine dioxide in the gel, but the systems with the highest levels of xanthan gum retained more chlorine dioxide than similar concentrations of guar gel. There are three possible reasons for this:
1. The higher viscosities help retain chlorine dioxide in the gel phase by reducing diffusion and consequent volatility.
2. The acid functionality on the xanthan gum polysaccharide polymer improves chlorine dioxide stability and encourages chlorine dioxide formation from any chlorite present in the mix.
3. Or a combination of reasons 1 and 2.
Following these observations, the inventor was able to demonstrate spontaneous generation of chlorine dioxide from aqueous solutions of solid 80% sodium chlorite and xanthan gum. While U.S. Pat. No. 3,741,805 cites the use of xanthan gum as a thickener for a sanitizing liquid prepared from a chlorine generator such as chlorinated trisodium phosphate, chlorinated isocyanurates or sodium hypochlorite (chlorite is not mentioned), this system is prepared at the time of use because xanthan gum gels do not have long term stability in the presence of the hypochlorite oxidizer present in the final solution. (See Kelco Bulletin, xe2x80x9cXanthan Gum, Natural biogum for scientific water control, fifth edition, page 11.)
There are several U.S. and foreign patents which describe chlorine dioxide gels which are prepared by mixing two gels at the time of use; one gel containing sodium chlorite precursor, and the other an organic acid such as lactic acid. U.S. Pat. No. 4,861,514 cites the preparation of compositions containing chlorine dioxide prepared from sodium chlorite and an initiator, with xanthan gum included in the list of possible initiators. In this respect, the reaction between chlorite and xanthan gum is not novel, but is cited to illustrate the benefit derived from the acid functionality of the xanthan gum in contributing to the stability of the chlorine dioxide gels. Using xanthan gum thickener, the generation of chlorine dioxide starting with dry 80% solid sodium chlorite is concentration sensitive. Increasing the level of solid 80% chlorite tenfold does not result in increased chlorine dioxide formation. As manufactured, this chlorite contains 20% inert diluents. Two of the components of the diluent are carbonate and caustic. These components will neutralize the organic acid functionality of the xanthan molecule and raise the pH of the system to the point where all the acidity is neutralized, at which point little or no chlorine dioxide is formed. The benefit of increased chlorite levels must be balanced against the increased alkalinity which accompanies the chlorite to the point where chlorite conversion is not totally inhibited. Use of liquid chlorite solutions in place of the dry sodium chlorite will pose similar problems since as manufactured, these solutions contain caustic added to stabilize the chlorite. The consequence of this chemistry is that preparation of chlorine dioxide gels by this route is limited to the formation of dilute gels containing at most only a few hundred parts per million chlorine dioxide. Novelty of the instant invention resides in the following features:
The chlorine dioxide already exists in its use concentration at the time the thickener is added.
Any conventional generation process can be used to prepare the chlorine dioxide.
The chlorine dioxide can be prepared by the dry mix process immediately prior to gel preparation.
The dry mix can contain the gelling agent so that gelling takes place during chlorine dioxide formation.
The attractiveness of the herein disclosed invention is that stable chlorine dioxide gels can be prepared directly in a single step by adding the appropriate thickeners to chlorine dioxide solution per se or the addition of chlorine dioxide solution to the gel, or by adding water to the dry mix containing the gelling agent.
Gels up to and including 6000 ppm are possible with the novel preparation method of this invention. The gels can be used for a broad spectrum of applications, from topical application to kill bacteria, viruses and fungi, to non-personal applications to control odors or sterilize enclosed spaces. Xanthan gum gels are very pleasant to the hand and can perform the function of lubrication during application. On drying, a thin film of solid xanthan remains at the pont of application.
Gels have also been formed by vigorous blending of sodium carboxymethylcellulose into aqueous chlorine dioxide. These gels can be prepared in extremely viscous form, and appear to be very stable, suffering chlorine dioxide loss by volatility only. These gels would be very well suited to applications where slow volatilization of chlorine dioxide is desired, such as atmospheric disinfection.
Xanthan gum is the preferred thickener because its acid functionality lowers gel pH and since chlorine dioxide is stable in an acid environment. Xanthan gum contributes to the stability of the chlorine dioxide in the gel.
While as a whole the main part of this invention was carried out with xanthan gum and guar gum, other gums would be operative as understood by those skilled in the art. Sodium caryboxymethylcellulose would be an operative gel. In addition, the main criteria for operative gums is the need for the gum to be stable and compatible with chlorine dioxide. The gum should be resistant to oxidation by the chlorine dioxide, and preferably the gel formed should have a low pH.
Because the chlorine dioxide is prepared at the use concentration before gelling, the final gel can contain any desired level of chlorine dioxide by adjusting the concentration of the aqueous chlorine dioxide solution prior to the addition of the gelling agent.
Once the chlorine dioxide gel is formed of the desired concentration, other additives such as colorants and stabilizers can be added, depending on the end use (e.g. disinfectant, deodorizer, etc.) as readily understood by those skilled in the art.
In its broadest aspect, this invention envisions a method for preparing a chlorine dioxide gel comprising the steps of preparing a solution of chlorine dioxide and adding said solution of chlorine dioxide to a gum thickener to form a gel containing chlorine dioxide, or alternatively the method for preparing a chlorine dioxide gel comprising the steps of preparing a solution of chlorine dioxide and adding a gum thickener to said solution of chlorine dioxide to form a gel containing chlorine dioxide.
In using the methods of this invention, a gel composition comprising a gel containing 1 to 5,000 ppm of chlorine dioxide can be prepared.
The herein disclosed invention contemplates a chlorine dioxide and gel product prepared by the process of preparing a solution of chlorine dioxide and adding said solution of chlorine dioxide to gum thickener or adding the gum thickener to the chlorine dioxide solution to form a concentrated chlorine dioxide gel composition.
The gels of this invention can form a disinfectant composition comprising a gel containing an effective amount of chlorine dioxide which can be used in a method of disinfecting comprising applying to the area to be disinfected a composition of a gel and chlorine dioxide wherein the chlorine dioxide is in the range of 1 to 5,000 ppm.